1. Field of the Invention
The present invention relates to a method and apparatus for charging a gas into a bag and more particularly to a method and apparatus for charging a gas into a gas compartment portion provided in a sealed side edge portion of a bag.
2. Description of the Related Art
Japanese Patent No. 4,771,785 describes a method and apparatus for charging a gas into a gas compartment portion of a bag in which a gas compartment portion is formed integrally and extends in the longitudinal direction in a sealed side edge portion of the bag.
More specifically in this gas filing method of Japanese Patent No. 4,771,785, an incision or an opening (collectively called “gas inlet”) that places the exterior of the bag in communication with the interior of the gas compartment portion is formed in the film sheet of a gas introduction section of the gas compartment portion, and the interior of the gas compartment portion is charged with gas by aligning the discharge outlet of a gas injection nozzle connected to a pressurized gas supply source with the gas introduction section, supporting the rear side of the bag equipped with gas compartment portion using a receiving member, and injecting gas from the gas injection nozzle into the gas compartment portion through the gas inlet. Further, while the injection is in progress, cramping is made to the gas introduction section or a blockage region in a vicinity thereof on both sides of the bag using a gas blocking gripper to thereby block the fluid communication of gas between the gas introduction section and the interior of the gas compartment portion, and, while cramping the blockage region with the gas blocking gripper, the bag is pressure-held on both sides of the gas introduction section by hot plates to heat-seal the gas introduction section so as to encapsulate the gas inside the gas compartment portion.
In Japanese Patent No. 4,771,785, when the gas injection nozzle is biased forward by a compression spring, and a discharge outlet at the distal end thereof is aligned with the gas introduction section of the gas compartment portion of the bag, the discharge outlet abuts the gas introduction section or the film sheet around it, the receiving member abuts the film sheet on the rear side, the compression spring is slightly compressed, and the two film sheets of the gas introduction section tightly adhere to each other. If gas discharge from the discharge outlet starts in this state, then under the gas pressure, the gas injection nozzle retreats against the bias of the compression spring, a small gap forms as a result between the discharge outlet and the receiving member, the gas introduction section expands under the pressure of the gas injected through the gas inlet, a space forms between the two film sheets of the gas introduction section, and gas is injected through this space into the gas compartment portion.
The method of Japanese Patent No. 5,104,073 is for a bag in which the gas compartment portion to be charged with gas through an incision or opening (collectively called “gas inlet”) formed at the upper edge of the gas compartment portion of a sealed side edge portion of a bag and in which an elongated (narrow) gas filling pathway is formed in the vicinity of (directly underneath) the area where the gas inlet is formed; and gas is injected through the gas inlet into the interior of the gas compartment portion, and, while the injection is in progress, heat sealing is performed for a part of the location of the filling pathway to seal the gas in the gas compartment portion.
In the gas charging method described in Japanese Patent No. 4,771,785, when acted upon by the pressure of the gas discharged from the discharge outlet of the gas injection nozzle, the gas injection nozzle slightly retreats against the bias of the compression spring, and as a result of which the gas introduction section is expanded by the compressed gas injected through the gas inlet, and a space forms between the two film sheets of the gas introduction section, thereby allowing gas injection into the gas compartment portion to be made. When this process is performed smoothly, the injection of gas into the gas compartment portion is accomplished within an extremely short period of time because the capacity of the gas compartment portion is not particularly large.
On the other hand, the distance that the gas injection nozzle retreats under the gas pressure varies depending on the pressure of the gas discharged from the discharge outlet of the gas injection nozzle and on the elastic force of the compression spring. This distance of retreat has a profound effect on the gas injection state, in other words, on the volume of gas entering the gas compartment portion per unit time and the pressure of the gas injected into the gas compartment portion. As a result, the time required for gas injection (or the efficiency of gas injection) and the degree of expansion of the gas compartment portion (or the pressure of the gas that fills the gas compartment portion) are profoundly influenced. For this reason, the setting of the pressure of the gas discharged from the gas injection nozzle and the elastic force of the compression spring, that is, the balancing of the two, needs to be done rigorously in order to obtain the optimum distance of retreat.
In addition, it is necessary to consider the possibility that the elastic force of the compression spring may decrease while the gas injection nozzle is used continuously. If the elastic force of the compression spring decreases even slightly, there is a possibility that the distance of retreat of the gas injection nozzle may change, the gas injection state may deteriorate (the volume of the gas entering the gas compartment portion per unit time may decrease and the pressure of the gas injected into the gas compartment portion may be reduced), and, furthermore, the gas may not getting into the gas compartment portion.
In particular, when a narrow, elongated gas charging pathway is formed at a location directly below the gas introduction section as in the bag equipped with a gas compartment portion described in Japanese Patent No. 5,104,073, then it is difficult for the gas injected into the gas compartment portion to escape, and it is also difficult to inject gas into the gas compartment portion, so that the above-described problems are particularly likely to occur.